Castle warfare was a grim and grisly business. If you’ve ever visited one of Britain’s magnificent castles, you’ve probably found yourself looking around and imagining what these conflicts were really like.

How long did a siege last? What kinds of weapons were used by attackers and what counter-measures could a castle’s inhabitants deploy? Did attackers really fling the corpses of captured enemies back over the walls? Is it true that castle defenders poured boiling water onto the attacking forces scaling ladders towards them?

If you’ve ever considered any of this, then we have the book for you. How To Attack A Castle (And How To Defend It) by Trevor Yorke is out now. The book is chock-full of illustrations and detailed descriptions that bring castle warfare vividly to life.

Rain of fire

Fire was used by attackers to destroy fortifications which contained timber structures. Lit torches or fires set up against a wooden wall were probably the earliest type of incendiary device.

Flaming arrows were used in the medieval period as, even after castle walls were built of masonry, there was still wood in the roofs and floors of stone buildings and lesser timber structures within the enclosure. The arrow could have been crudely assembled with a strip of material soaked in pitch, oil or resin wrapped around the shaft. More sophisticated arrowheads were designed with metal cages for coal, wood shavings, cloth or similar materials soaked in oil, which were then lit and fired.

A more potent weapon which struck fear into the hearts of defenders was ‘Greek fire’, a petroleum-based mixture which could not be extinguished with water. The knowledge for making this mixture (an early form of napalm) came via the Crusades to the Middle East in the 11th century where siege warfare was far more advanced than it was in Western Europe.

Death from below

November, 1215. Depicted below is the moment when, after nearly two months of besieging Rochester Castle, Kent, military miners working for King John finally brought down the corner of the mighty stone keep.

The king’s forces had attacked the defences with crossbows and missiles, and bombarded its walls with siege engines. But, it was only when they undermined its fortifications by digging tunnels beneath the structure that they finally broke through.

The image below shows how this was done.

Sappers (under the lean-to structure known as a sow or penthouse) removed masonry from the corner of a tower and at the same time inserted timbers to support the wall. They would then start a fire in the gap, giving them time to escape before the supports burn through sending the wall above crashing down. Beneath the ground miners have dug a tunnel under another section of wall and are bringing through kindling in order to create a fire. This should create a gap above once the flames have burnt through the timbers or have cracked the foundations. Sometimes the defending castellan was invited to inspect works like this in the hope the garrison would surrender before the walls were destroyed. This was a crafty move as the successful attackers would then be the ones who would have to repair them.

Anatomy of a siege tower

A siege tower or belfry was a tall timber structure which could either be a stationary platform to give attackers a better range of fire or a mobile structure with a drawbridge to enable them to get upon the battlements as shown here.

This tall example has an upper gallery allowing archers to force back defenders as the men pour out onto the walls. These mobile towers would have been pulled and pushed by oxen or groups of men on wheels or rolled on logs, over an embankment across the moat made of bundles of branches and sticks in order to reach the walls. All the time it was being moved defenders would try and damage it with stones or set it alight with fire arrows, hence it needed to be covered in wet hides or other forms of sheeting to reduce the risk.

The longest siege

Pictured here is the 1266 siege of Kenilworth Castle, the longest and most expensive ever undertaken in medieval Britain.

Nobles had rebelled against King Henry III, and after their leader Simon de Montfort was killed in battle at Evesham, the remaining forces retreated to their Kenilworth stronghold.

The siege lasted around six months with the King’s forces building siege towers, mounting an attack by boat and pounding the walls and interior with the latest stone-throwing machines to such an intensity at one point that the projectiles were said to have smashed into each other in mid-air. Yet all these failed and they had to wait it out until disease and shortages of food forced the garrison to surrender in December.

Bringer of death, destruction & disease: the mighty trebuchet

The trebuchet seems to have developed in the Middle East before the mid 12th century. The first use in this country was probably by Prince Louis during his invasion of England in 1215. At one end was a sling in which the stone ball was held, which ran within a grooved slot in the base of the frame to help it maintain an accurate line as it was fired.

The stone balls usually weighed between 40 and 100kg (90-220lbs) and could be thrown a distance of 300-400 yards which could keep larger types out of the reach of archers defending the castle. As these siege engines could throw projectiles high into the interior of the castle, more gruesome objects like severed heads to demoralise the garrison, or rotting animals to spread disease were used.

Longbows vs crossbows

This detail from a famous medieval illustration of the Battle of Crécy in 1346 from Jean Froissart’s Chronicles shows the French on the left with crossbows and the English on the right with longbows.

Crossbows had long been an effective weapon for the defence of castles. The exact origins of the longbow are unknown, but the Welsh armies had perfected its use and after the conquest of Wales it was adopted by the English. In its fully developed form it was 1.8 - 2.1m (6’ - 6’10’) long, made from yew, ash or elm, with strings made from hemp, linen, silk, sinew or rawhide and attached at the top and bottom by nocks, often made from the tip of an animal horn. They were very powerful weapons able to fire a greater distance than crossbows, around 230m (251 yards), the length of two football pitches end on, although even longer distances are recorded. Arrows could be shot at a rate of up to 12 per minute and some could pierce armour, making this one of the most lethal medieval weapons. However, it took great skill and strength to fire. Longbowmen’s skeletons are recognisable due to the extra bone which developed in one arm and defects in their shoulders and wrists. Its principal use was on the battlefield where it could be fired high to rain arrows down upon the enemy but it was also used in the defence and attack of castles during the 14th and 15th century alongside short bows and crossbows.

The art of deception

As castle defences became ever more advanced so other methods of attack were used. The Scots under Robert the Bruce could not match the English for firepower so they used deception to take a number of castles; a clever solution which limited the loss of life and saved a fortune on machinery. At Linlithgow Castle in 1313 the Bruce sent a local merchant up to the castle with a cart piled full of hay. As he was let in the cart stopped in the castle gateway so it could not be shut. The Scots then stormed the castle and massacred the garrison inside. One night at Roxburgh in 1314, a number of Bruce’s men threw black cloaks over themselves and approached the castle on all fours so the defenders in the dim light thought they were grazing cattle. When a few got close enough they threw off their cloaks and scaled the walls and threw open the gates so the rest of their force could take the castle.